#box{
    height: 200px;
    width: 200px;
    color: red;
    background: green;
    display: flex;
    backface-visibility: hidden;
    /*background: url("../imgs/51.png") no-repeat 100%;*/
    background: red;
}
.nav{
    width: 200px;
    background: green;
}
header{
    height: 200px;
    background: red;
}
/*
#box{
    height: 200px;
    width: 200px;
    color: red;
    background: green;
    display: flex;
    backface-visibility: hidden;
}*/
